The invention relates to a method and an apparatus for processing of two d.c. voltages, especially representing unbalance components.
German Patent No. 1,108,475 discloses a method for determining the unbalance of a rotational body. According to said known method, two square wave voltages are produced which are phase shifted relative to each other and which are then mixed with each other. These square wave voltages are produced from two voltages which are stored as analog values and which represent the unbalance components of the rotational body to be balanced. The square wave voltages have actually a stairstep shaped wave form and according to the known method the fundamental sine wave is filtered out of the stairstep signal, whereby the amplitude of the fundamental sine wave is proportional to the unbalance and whereby the phase position of the fundamental wave relative to one of the square wave voltages represents the unbalance angle, which is an angle defining the angular position of the unbalance on the rotational body relative to a reference mark.
The above described prior art method has the disadvantage that it is not too precise, especially with regard to the indication of the unbalance angle, because several method steps must be performed in sequence in order to ascertain the unbalance vector and because a precisely tuned and constant filter is required. Filters do not tend to retain their characteristics precisely, especially where temperature changes must be taken into account. Thus, the ascertaining and display of the polar unbalance information, especially of the angular position of the unbalance is necessarily subject to errors. Furthermore, the known method does not provide any possibility for directly storing the unbalance angle, rather, said angle can only be retained indirectly through the component direct voltages. As a result, additional angular errors may occur, especially as time passes and such additional angular errors may substantially influence the total error. This is so, as it is known, that the error occurring during the ascertaining, the storing and the display of the unbalance angle enters into the total error more strongly than the unbalance value itself, namely, by a factor of 2.pi..